In history class, the girl to boy ratio is $7$ to $10$. If there are $14$ girls, how many boys are there?
A ratio of $7$ girls to $10$ boys means that there is a group of $7$ girls for every group of $10$ boys. If there are $14$ girls, then there are $2$ groups of $7$ girls each. Because we know the ratio is $7:10$ , there must be $2$ groups of $10$ boys each. There is a total of $20$ boys in history class.